Papers by Author: Valentin V. Emtsev

Abstract: Deep states produced during γ irradiation of germanium have been compared with the defects produced by 1 and 3MeV silicon ion implantation. The deep states have been studied using DLTS and Laplace DLTS techniques. Isochronal annealing has been used to investigate the defect evolution and stability over the range 100 to 500°C. It is found that while irradiation damage can be removed with a very low thermal budget, the implantation damage is more complex and much more difficult to remove. By comparing low (1010cm-2) and high (1012cm-2) implantation doses it appears that both the complexity and stability of defects increases with increasing dose. Similar experiments have been performed on Ge rich Si1-xGex (x=0.992). The focus of this work has been on vacancy related defects. It is believed that the diffusion of both acceptors and donors is vacancy mediated in Ge and so vacancy clusters rather than interstitial clusters are expected to be the technologically significant defect in enhanced diffusion. The significance in terms of junction leakage and generation currents are discussed in the paper in the context of the observed defect reactions.

Abstract: Cz-grown, carbon-doped silicon samples were irradiated by fast neutrons. We investigated the annealing behaviour of oxygen-related defects, by infrared spectroscopy. We studied the reaction channels leading to the formation of various VmOn defects and in particular the VOn defects formed by the accumulation of oxygen atoms and vacancies in the initially produced by the irradiation VO defects, as the annealing temperature ramps upwards. We mainly focused on bands appearing in the spectra above 450 oC. A band at 1005 cm-1 is found to be the convolution of two bands at 1004 and 1009 cm-1. The latter band has the same thermal stability with the 983 cm-1 of the VO4 defect and therefore is also attributed to this defect. The former band has the same thermal stability with three other bands at 965, 1034 and 1048 cm-1. These four bands may be attributed to VOn (n=5,6) defects, although other VmOn complexes are also potential candidates. Furthermore, we found that pre-treatments of the samples at 1000 oC, with or without the application of high hydrostatic pressure lead to an increase in the concentration of the VO2, VO3 and generally VOn defects in comparison with that of the untreated samples.

Abstract: Effects of compressive stress on oxygen agglomeration processes in Czochralski grown silicon heat treated at T= 450OC, used as a reference temperature, and T= 600OC to 800OC are investigated in some detail. Compressive stresses of about P= 1 GPa lead to enhanced formation of Thermal Double Donors in materials annealed over a temperature range of T= 450OC – 600OC. It has been shown that the formation of thermal donors at T= 450OC under normal conditions and compressive stress is accompanied with loss of substitutional boron. In contrast, the concentration of the shallow acceptor states of substitutional boron in silicon annealed under stress at T≥ 600OC remains constant. An enhancement effect of thermal donor formation is gradually weakened at T≥ 700OC. The oxygen diffusivity sensitive to mechanical stress is believed to be responsible for the observed effects in heat-treated silicon.

Abstract: A comparison study of radiation damage in n-type silicon grown by the floating zone technique and n-type silicon carbide grown by the sublimation epitaxy technique was carried out for the first time under the same irradiation conditions. This comparison is drawn for an energy region of fast electrons at ≈ 1 MeV where Frenkel pairs as primary defects, i e the self-interstials bound to their parent vacant sites at a distance of a few lattice spacings, are produced most effectively. The removal rates of charge carriers in n-Si and n-SiC (4H and 6H) were found to be about 0.23 cm-1 and 0.015 cm-1, respectively. The possible reasons of the observed difference are briefly discussed.